An airport ground staff member was jailed for three years for helping unauthorised passengers to board planes with forged documents in what a judge termed a deterrent sentence to underline the severity of the offence.

Judge Albert Wong Sung-hau said the actions of Chau Pak-kin, 27, had undermined the effectiveness of immigration control at Chek Lap Kok airport and compromised Hong Kong's reputation as an international city.

In the District Court, the judge said Chau had also jeopardised the safety of the planes and their destination countries by assisting the stowaways, which included a young mainlander disguised as an elderly Caucasian.

Chau was convicted of conspiracy to obtain services by deception. Another defendant, Chan Wing-chung, 27, was acquitted on Monday due to insufficient evidence.

Wong accepted that Chau did not take an active part in the conspiracy but said that in agreeing to turn a blind eye to unauthorised passengers, he had been instrumental to the success of the stowaways as he was the very last barrier to prevent them passing through the boarding gates.

Wong also said Chau had failed to deliver on his duty to check the boarding passes and documents of passengers carefully and had shown a severe breach of trust to his employer, Singapore Air Terminal Services.

But the judge accepted that Chau, who had been involved in two of four stowaway operations, had not received any reward, although he could not offer an explanation for deposits in his bank account, the amount of which was not disclosed in court.

In mitigation, barrister Jacky Jim Chun-ki submitted a letter in which Chau said he felt remorseful for what he had done and sorry for his family and friends who had worried about him. He said Chau had taken the initiative to withdraw from the plot by resigning from Singapore Air Terminal Services in December.

But the judge pointed out that Chau had failed to perform his duties for more than half a year, despite knowing how unlawful and serious the matter was.